In all kinds of conventional IC packages, warpage is a serious problem existing at various interfaces during packaging processing or in packages.
As shown in FIG. 1, a window BGA 100 utilizes a substrate 110 having a slot 111 to carry a chip 120 by a die-attaching material 122. The bonding pads 121 of the chip 120 are electrically connected to the substrate 110 by a plurality of bonding wires 150. Then the chip 120 is encapsulated by an encapsulant 130. Moreover, a plurality of external terminals 140 such as solder balls are disposed under the substrate 110 for outer electrical connection. Since the slot 111 of the substrate 110 is formed and aligned to the center line 113 of the substrate 110 and is longer than the chip 120 for filling the slot 111 with the encapsulant 130. Since both extensions 111A of the slot 111 are not covered by the chip 120, therefore, the encapsulant 130 flowing from the top molding gate 112 will be formed on the top surface of the substrate 110 and also be formed in the slot 111 through the extensions 111A. As shown in FIG. 1, the encapsulant 131 at bottom encapsulates the bonding wires 150. However, the encapsulant 130 and its bottom part 131 are the same molding compound, therefore, there is no reinforcement effect. After molding, the encapsulant 130 is under curing shrinkage, therefore, there is warpage in the IC package 100, especially, at the cross section along the center line 113 as shown in FIG. 3.
A conventional IC package is disclosed to use two encapsulants with different materials to reduce the warpage due to temperature variations such as thermal cycle tests at the interfaces. Since the two different materials of the encapsulant are formed on the same substrate and are connected to each other, therefore, different molding processes and separated curing steps are needed. Therefore, the warpage due to the curing shrinkage of the encapsulant can not be avoided. Furthermore, since the first encapsulant is overlapped on the second encapsulant, the overall thickness of an IC package will increase.
Another known IC package is disclosed, where an internal encapsulant, a heat spreader, and an external encapsulant are formed on a substrate. The heat spreader covers the internal encapsulant and the external encapsulant formed around the heat spreader where the modulus of the external encapsulant is higher than the internal encapsulant. The heat spreader is a key component to completely cover the chip and to separate the internal encapsulant and the external encapsulant. The warpage still exists due to the curing shrinkage for both internal encapsulant and external encapsulant during molding process.